326 MALACOZOA. GASTEROPODA. PECTINIBRANCHIATA. 



the mouth white, but not pearly, and a white worn space ex- 

 tending from it to the margin ; when decorticated however either 

 on the exterior or interior, the surface nacreous and shining. 

 Length nine-twelfths of an inch, diameter ten-twelfths. 



The ahove description from two specimens, found near 

 Peterhead, in January, 1 843, and sent by Roderick Gray, Esq. 



Trochus crassus. Mont. Test. Brit. 281. Trochus crassus. 

 Flern. Brit Anim. 323. 



GENUS 4. LITTORINA. P. 54, 135. 

 Littorina jugosa. Ridged Periwinkle. 



Shell subovato-conical, thick, with, the spire a third 

 of the length of the last turn, which is tumid in the 

 middle, and marked with ten or twelve elevated, thin, 

 spiral ridges ; the aperture roundish, purplish-brown, 

 the outer lip thin. Jugosus, ridged. 



Shell somewhat ovato-fusiform, thick ; with the spire from 

 a fourth to a third of the whole length, and tapering to a 

 small point ; the whorls four, rather flat on the spire, with 

 the suture distinct ; the last turn very large, ventricose, with 

 ten or twelve prominent, sharpish, spiral ridges, and incon- 

 spicuous transverse striae, the colour dusky, yellow, or whitish ; 

 the aperture roundish, with the outer lip bevelled, and marked 

 externally by the spiral grooves, the inner reflexed, the inte- 

 rior purplish-brown. Length four twelfths of an inch, breadth 

 three and a-half twelfths. 



It differs from Littorina littorea in its form, and especially 

 its strong grooves and ridges ; but it is more allied to that 

 species than to Littorina rudis, and differs, I think, from 

 both species, its characters being in fact more prominent than 

 those of most species of its genus. 



On the .rocky coasts, near low-water mark ; and in shell 

 sand on the beaches; not uncommon. 



Turbo jugosus. Mont. Test. Brit. 586. PL 20. f. 2. Turbo 

 jugosus. Turt. Diet. 



GENUS 6. TURBONILLA. 



Shell turrite, with the spire very elongated, tapering 

 to a fine point ; the aperture subovate, entire, with the 

 peristome incomplete behind, the outer lip thin, the 

 inner nearly straight, reflexed, leaving a small umbilicus. 

 Turbonilloy diminutive of Turbo. Risso. 



